Re: Problems with scsi emulation

From: Jonathan Woithe (
Date: Thu Jun 05 2003 - 23:18:03 EST

Doug Gilbert wrote:
> Due to many problems with DMA locking up on ATAPI writers
> earlier in the lk 2.4 series, Linux takes a very
> conservative approach and turns off DMA.

Really? That doesn't seem to be the case with my ATAPI CD writer under stock
2.4.20. At the start of this year I found that DMA was turned on by default
for my writer AND that having DMA turned on was usually fatal for burning (a
kernel oops would occur). For reference an earlier posting of mine to lkml:

> It can be turned back on with:
> # hdparm -d 1 /dev/hdb

I found that to ensure a reliable CD writing, I had to manually turn DMA OFF
under stock 2.4.20 just to get reliable writing. If I have DMA on I can
almost guarantee a kernel oops before the CD is complete under 2.4.20.

Given that the original correspondant was using Redhat 9.0, I'm guessing
that the advise about turning DMA back on refers to the Redhat
custom kernel in Redhat 9.0 as opposed to stock 2.4.20. In my experience
DMA just doesn't work in stock 2.4.20 for what it's worth.


* Jonathan Woithe                        *
*                      *
** "Time is an illusion; lunchtime doubly so"                              **
*  " wouldn't recognize a subtle plan if it painted itself purple and *
*   danced naked on a harpsichord singing 'subtle plans are here again'"    *
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